1. Field of the Invention
The present invention relates to the field of integrated circuits. In particular, the invention relates to monitoring at least one of an operating temperature and an operating voltage of an integrated circuit.
2. Description of the Prior Art
The signal propagation delay through elements of an integrated circuit may vary over time in response to changes in operating temperature or operating voltage of the integrated circuit. Also, the signal propagation delay can vary from circuit to circuit due to variation in process conditions when manufacturing the circuit (for example changes in temperature or humidity during the manufacturing process). Therefore, the performance of an integrated circuit may vary from time to time and between different circuits or different regions of a circuit. A monitoring circuit may be provided to monitor changes in operating conditions, to gain visibility of the likely performance of the integrated circuit. For example, the monitoring circuit may be placed in a region of interest of the integrated circuit and may measure the propagation delay through a replica circuit element, which can be assumed to track the delay through real circuit elements of the surrounding region of the integrated circuit.
One problem with such monitoring circuits is that it can be difficult for a monitoring circuit to distinguish a change in operating temperature from a change in operating voltage. A decrease in operating temperature and an increase in operating voltage both tend to speed up the propagation speed of signals in a typical monitoring circuit, and so it can be difficult to determine the relative contribution of temperature and voltage for a given change in propagation speed. The present technique seeks to provide a monitoring circuit which can distinguish changes in operating temperature from changes in operating voltage.